Nowadays, the information and communication technologies implementing information transmission, reception and processing systems, particularly in the form of digital signals, require infrastructures and switching centers with apparatuses having a high density and capacity. The required capacity values can be obtained only by using an optical fiber transmission technology, by virtue of the transmission band width offered by the optical fibers.
The apparatuses composing the switching centers at the nodes of a communication network typically include a plurality of signal switching boards, assembled to an electrical interconnection and mechanical support board that is referred to as a “backplane”. The physical connection (interconnection) between the boards is implemented by one or more optical fiber interconnection circuits assembled on the backplane or in the proximity thereof, arranged to connect each board to all the other ones, according to a full-mesh connection architecture.
The prior art for implementing the interconnection systems at the switching nodes of a network is based on assembling the switching boards on a side of the backplane by suitable connectors, and on the arrangement of outer, flexible, optical interconnection circuits on the opposite side of the backplane, as schematically shown in FIG. 1, where the switching boards in a cabinet C of a telephonic switching center are indicated with S, the backplane board is indicated with B, and the rear interconnection circuit is indicated with I.
Examples of commercial interconnection circuits that have characteristic of easiness of handling and reduced overall dimensions in the arrangement of optical interconnection conductors are the product FlexPlane by Molex, www.molex.com and the product LIGHTRAY OFX by Tyco Electronics, www.te.com.
Such interconnection circuit, schematically shown in FIG. 2, comprises a first plurality of fiber optic ribbons R1-R8 at a first end portion, and a corresponding second plurality of fiber optic ribbons R1′-R8′ at a second opposite end portion, in which each ribbon is crimped at an end with terminal devices for the mechanical and electro-magnetic coupling to the backplane connectors.
Each fiber optic ribbon Ri includes a preset number of fibers Fi (i=1, n), where n is typically equal to 8, 12, 16, 32, aligned parallel along a longitudinal extension axis of the ribbon in a planar arrangement, bundled and held in place by a sheath G, as schematically represented in FIG. 3.
In the interconnection circuit, the ribbons have, downstream of the corresponding terminal, a portion embedded in a case L that is mechanically more rigid than the optical fibers, within which they are unsheated, thus releasing the single optical fibers, which are routed separately, each towards a different connector on the opposite side. The routing circuit of optical fibers that is formed in the case L keeps a suitable flexibility, which allows assembling the ribbon terminals to the backplane connectors.
This technique is described, for example, in WO 2005/114286 A1, US 2008/002936 A1, and in WO 02/63365, and in the publication “Flexible High Density Optical Circuits”, by Muhammed A. Shahid, Peng Wang, Jeffery H. Hicks, OFS, 2000 Northeast Expressway, Norcross, Ga. 30071 (www.ofsoptics.com). The routing of the circuit, i.e., the separation of the fibers from the ribbons and the routing towards another connector of the single fibre, subsequently embedded in another ribbon, are carried out, for example, by means of the apparatus as described in EP 1 182 483 A1.
However, these solutions have the drawbacks of a complex implementation and a not easy maintenance, since a failure in a fiber requires, in fact, to replace the entire flexible circuit and the corresponding connectors.
US 2007/0154160 A1 proposes a device implementing a controlled deformation (specifically, a folding) of a fiber optic ribbon associated with a backplane board, so that it is possible to build a connection end for assembling switching boards orthogonal to the backplane, while, on the backplane board side opposite to the connection end, the fiber optic ribbon extends parallel to the backplane board plane, so as to implement an interconnection circuit with minimum overall dimensions.
However, this document does not completely deal with the technical problem of implementing a complete interconnection system that has reduced overall dimensions and with an easy maintenance in the case of failures in an optical fiber, and it does not teach how to implement a complete interconnection circuit while developing a plurality of fiber optic ribbons on a backplane board to ensure the mutual interconnection of an ordered arrangement of connectors suitable to receive a plurality of switching boards.